Solid-state electronic device including dielectric bismuth niobate film formed from solution

ABSTRACT

A solid-state electronic device according to the present invention includes: an oxide layer (possibly containing inevitable impurities) that is formed by heating, in an atmosphere containing oxygen, a precursor layer obtained from a precursor solution as a start material including both a precursor containing bismuth (Bi) and a precursor containing niobium (Nb) as solutes, the oxide layer consisting of the bismuth (Bi) and the niobium (Nb); wherein the oxide layer is formed by heating at a heating temperature from 520° C. to 650° C.

TECHNICAL FIELD

The present invention relates to a solid-state electronic device.

BACKGROUND ART

There has been conventionally developed a thin film capacitorexemplifying a solid-state electronic device and including aferroelectric thin film that possibly enables high speed operation.Metal oxide is now often considered as a dielectric material included ina capacitor, and the sputtering technique is widely adopted as a methodof forming the ferroelectric thin film (Patent Document 1).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP 10-173140 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, it is generally necessary to bring the inside of a film formingchamber into a high vacuum state in order to achieve fine film qualityin the sputtering technique. The vacuum process or the photolithographytechnique other than the sputtering technique also typically requiresrelatively long time and/or expensive equipment. These processes lead toquite low utilization ratios of raw materials and production energy.When adopting the production method described above, production of asolid-state electronic device requires many steps and long time, whichis not preferred from the industrial and mass productivity perspectives.The conventional technique also causes the problem that increase in areais relatively difficult to achieve.

Selection of a material having the high properties as an insulatinglayer of a solid-state electronic device, which is produced inaccordance with an excellent method from the industrial and massproductivity perspectives, is thus also one of the technical objects tobe achieved for improvement in performance of the solid-state electronicdevice.

The present invention achieves this object to enable simplification andenergy saving in a process of producing a solid-state electronic device.The present invention thus contributes remarkably to provision of asolid-state electronic device that is excellent from the industrial andmass productivity perspectives.

Solutions to the Problems

The inventors of this application have gone through intensive researcheson oxide that can be included in a solid-state electronic device such asa capacitor or a thin film capacitor as well as can be formed even inaccordance with an inexpensive and simple method. The inventors havefound, through many trials and tests, that a specific oxide materialreplacing conventionally and widely adopted oxide is relativelyinexpensive, simplifies the production steps, has relatively highinsulation and relative permittivity, and can be included also in asolid-state electronic device. The inventors have also found that theoxide enables patterning in accordance with an inexpensive and simplemethod adopting the “imprinting” technique also called “nanoimprinting”.The inventors thus found that it is possible to form a layer of theoxide and produce a solid-state electronic device including such oxidelayers in accordance with a process that achieves remarkablesimplification or energy saving as well as facilitates increase in areain comparison to the conventional technique. The present invention hasbeen devised in view of these points.

A solid-state electronic device according to a first aspect includes: anoxide layer (possibly containing inevitable impurities) that is formedby heating, in an atmosphere containing oxygen, a precursor layerobtained from a precursor solution as a start material including both aprecursor containing bismuth (Bi) and a precursor containing niobium(Nb) as solutes, the oxide layer consisting of the bismuth (Bi) and theniobium (Nb); wherein the oxide layer is formed by heating at a heatingtemperature from 520° C. to 650° C.

In the solid-state electronic device according to a second aspect, theoxide layer has a carbon content percentage of at most 1.5 atm %.

In the solid-state electronic device according to a third aspect, theprecursor layer is provided with an imprinted structure by imprintingthe precursor layer while the precursor layer is heated at a temperaturefrom 80° C. to 300° C. in an atmosphere containing oxygen before theoxide layer is formed.

In the solid-state electronic device according to a fourth aspect, theimprinting is performed with a pressure in a range from 1 MPa to 20 MPa.

In the solid-state electronic device according to a fifth aspect, theimprinting is performed using a mold that is preliminarily heated to atemperature in a range from 80° C. to 300° C.

The solid-state electronic device according to a sixth aspect is acapacitor.

The solid-state electronic device according to a seventh aspect is asemiconductor device.

The solid-state electronic device according to an eighth aspect is aMEMS device.

Effects of the Invention

In the solid-state electronic device according to the first aspect, theoxide layer can be formed through a relatively simple process not inaccordance with the photolithography technique (but in accordance withthe ink jet technique, the screen printing technique, theintaglio/relief printing technique, or the nanoimprinting technique).There is thus no need to include a process requiring relatively longtime and/or expensive equipment, such as the vacuum process, a processin accordance with the photolithography technique, or the ultravioletirradiation process. Moreover, the oxide layer is formed through heattreatment at a relatively low temperature with no need for any of theabove processes. The solid-state electronic device is thus excellentfrom the industrial and mass productivity perspectives.

The solid-state electronic device according to the second aspectachieves decrease in leakage current.

In the solid-state electronic device according to the third aspect,deterioration in plastic deformability of each precursor layer can beprevented quite reliably during imprinting, so that the desiredimprinted structure can be formed with higher accuracy.

In the solid-state electronic device according to the fourth aspect, thedesired imprinted structure can be formed with high accuracy.Furthermore, the pressure applied for imprinting is in such a low rangefrom 1 MPa to 20 MPa. The mold is thus less likely to be damaged uponimprinting and increase in area can be also achieved advantageously.

As the solid-state electronic device according to the sixth aspect, itis possible to provide the capacitor that is excellent from theindustrial and mass productivity perspectives.

As the solid-state electronic device according to the seventh aspect, itis possible to provide the semiconductor device that is excellent fromthe industrial and mass productivity perspectives.

As the solid-state electronic device according to the eighth aspect, itis possible to provide the MEMS device that is excellent from theindustrial and mass productivity perspectives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an entire configuration of a thin film capacitorexemplifying a solid-state electronic device according to a firstembodiment of the present invention.

FIG. 2 is a sectional schematic view of a process in a method ofproducing the thin film capacitor according to the first embodiment ofthe present invention.

FIG. 3 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the first embodiment ofthe present invention.

FIG. 4 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the first embodiment ofthe present invention.

FIG. 5 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the first embodiment ofthe present invention.

FIG. 6 is a sectional schematic view of a process in a method ofproducing a thin film capacitor according to a second embodiment of thepresent invention.

FIG. 7 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the second embodiment ofthe present invention.

FIG. 8 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the second embodiment ofthe present invention.

FIG. 9 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the second embodiment ofthe present invention.

FIG. 10 is a view of an entire configuration of the thin film capacitorexemplifying a solid-state electronic device according to the secondembodiment of the present invention.

FIG. 11 is a view of an entire configuration of a thin film capacitorexemplifying a solid-state electronic device according to a thirdembodiment of the present invention.

FIG. 12 is a sectional schematic view of a process in a method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 13 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 14 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 15 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 16 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 17 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 18 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 19 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 20 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 21 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the third embodiment ofthe present invention.

FIG. 22 is a sectional schematic view of a process in a method ofproducing a thin film capacitor according to a fourth embodiment of thepresent invention.

FIG. 23 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the fourth embodiment ofthe present invention.

FIG. 24 is a sectional schematic view of a process in the method ofproducing the thin film capacitor according to the fourth embodiment ofthe present invention.

FIG. 25 is a view of an entire configuration of the thin film capacitorexemplifying a solid-state electronic device according to the fourthembodiment of the present invention.

FIGS. 26( a) and 26(b) are a cross-sectional TEM picture and an electronbeam diffraction image each showing a crystal structure of an oxidelayer serving as an insulating layer in the first embodiment of thepresent invention.

FIGS. 27( a) and 27(b) are a cross-sectional TEM picture and an electronbeam diffraction image each showing a crystal structure of an oxidelayer serving as an insulating layer in a comparative example.

DESCRIPTION OF REFERENCE SIGNS

-   -   10 substrate    -   20,220,320.420 lower electrode layer    -   220 a,320 a,420 a lower electrode layer precursor layer    -   30,230,330.430 oxide layer    -   30 a,230 a,330 a.430 a oxide layer precursor layer    -   40,240,340.440 upper electrode layer    -   240 a,340 a,440 a upper electrode layer precursor layer    -   100,200,300,400 thin film capacitor exemplifying solid-state        electronic device    -   M1 lower electrode layer mold    -   M2 insulating layer mold    -   M3 upper electrode layer mold    -   M4 stacked body mold

EMBODIMENTS OF THE INVENTION

A solid-state electronic device according to each of the embodiments ofthe present invention is described in detail with reference to theaccompanying drawings. In this disclosure, common parts are denoted bycommon reference signs in all the drawings unless otherwise specified.Furthermore, components according to these embodiments are notnecessarily illustrated in accordance with relative scaling in thedrawings. Moreover, some of the reference signs may not be indicated forthe purpose of easier recognition of the respective drawings.

First Embodiment 1. Entire Configuration of Thin Film CapacitorAccording to the Present Embodiment

FIG. 1 is a view of an entire configuration of a thin film capacitor 100exemplifying a solid-state electronic device according to the presentembodiment. As shown in FIG. 1, the thin film capacitor 100 includes asubstrate 10, a lower electrode layer 20, an oxide layer 30 serving asan insulating layer made of a dielectric substance, and an upperelectrode layer 40. The lower electrode layer 20, the oxide layer 30,and the upper electrode layer 40 are stacked on the substrate 10 in thisorder.

The substrate 10 can be made of any one of various insulating basematerials including highly heat resistant glass, an SiO₂/Si substrate,an alumina (Al₂O₃) substrate, an STO (SrTiO) substrate, an insulatingsubstrate obtained by forming an STO (SrTiO) layer on a surface of an Sisubstrate with an SiO₂ layer and a Ti layer being interposedtherebetween, and a semiconductor substrate (e.g. an Si substrate, anSiC substrate, or a Ge substrate).

The lower electrode layer 20 and the upper electrode layer 40 are eachmade of any one of metallic materials including high melting metal suchas platinum, gold, silver, copper, aluminum, molybdenum, palladium,ruthenium, iridium, or tungsten, alloy thereof, and the like.

In the present embodiment, the insulating layer made of a dielectricsubstance is formed by heating, in an atmosphere containing oxygen, aprecursor layer obtained from a precursor solution as a start materialincluding both a precursor containing bismuth (Bi) and a precursorcontaining niobium (Nb) as solutes (hereinafter, a production methodincluding this step is also called the solution technique). There isthus formed the oxide layer 30 consisting of bismuth (Bi) and niobium(Nb) (possibly containing inevitable impurities). Furthermore, as to bedescribed later, the present embodiment is characterized in that aheating temperature (a main baking temperature) for forming the oxidelayer is set in the range from 520° C. to 650° C. The oxide layerconsisting of bismuth (Bi) and niobium (Nb) is also called a BNO layer.

The present embodiment is not limited to this structure. Moreover,patterning of an extraction electrode layer from each electrode layer isnot illustrated in order to simplify the drawings.

2. Method of Producing Thin Film Capacitor 100

Described next is a method of producing the thin film capacitor 100.Temperatures indicated in this application are preset temperatures of aheater. FIGS. 2 to 5 are sectional schematic views each showing aprocess in the method of producing the thin film capacitor 100. As shownin FIG. 2, the lower electrode layer 20 is initially formed on thesubstrate 10. The oxide layer 30 is then formed on the lower electrodelayer 20, and the upper electrode layer 40 is subsequently formed on theoxide layer 30.

(1) Formation of Lower Electrode Layer

FIG. 2 shows the step of forming the lower electrode layer 20. Thepresent embodiment exemplifies a case where the lower electrode layer 20in the thin film capacitor 100 is made of platinum (Pt). The lowerelectrode layer 20 made of platinum (Pt) is formed on the substrate 10in accordance with the known sputtering technique.

(2) Formation of Oxide Layer Serving as Insulating Layer

The oxide layer 30 is then formed on the lower electrode layer 20. Theoxide layer 30 is formed through (a) the step of forming andpreliminarily baking the precursor layer and then (b) the main bakingstep. FIGS. 3 and 4 each show the step of forming the oxide layer 30.The present embodiment exemplifies a case where the oxide layer 30 isformed using oxide consisting of bismuth (Bi) and niobium (Nb) in thesteps of producing the thin film capacitor 100.

(a) Formation and Preliminary Baking of Precursor Layer

As shown in FIG. 3, formed on the lower electrode layer 20 in accordancewith the known spin coating technique is a precursor layer 30 a obtainedfrom a precursor solution as a start material including both a precursorcontaining bismuth (Bi) and a precursor containing niobium (Nb) assolutes (called a precursor solution; hereinafter, this applied to asolution of a precursor). Examples of the precursor containing bismuth(Bi) for the oxide layer 30 possibly include bismuth octylate, bismuthchloride, bismuth nitrate, and any bismuth alkoxide (e.g. bismuthisopropoxide, bismuth butoxide, bismuth ethoxide, or bismuthmethoxyethoxide). Examples of the precursor containing niobium (Nb) forthe oxide layer 30 in the present embodiment possibly include niobiumoctylate, niobium chloride, niobium nitrate, and any niobium alkoxide(e.g. niobium isopropoxide, niobium butoxide, niobium ethoxide, orniobium methoxyethoxide). The precursor solution preferably includes asolvent of one alcohol selected from the group consisting of ethanol,propanol, butanol, 2-methoxyethanol, 2-ethoxyethanol, and2-butoxyethanol, or a solvent of one carboxylic acid selected from thegroup consisting of acetic acid, propionic acid, and octylic acid.

The preliminary baking is then performed in the oxygen atmosphere or inthe atmosphere (collectively called an “atmosphere containing oxygen”)for a predetermined time period at a temperature in the range from 80°C. to 250° C. The preliminary baking sufficiently evaporates the solventin the precursor layer 30 a and causes a preferred gel state forexerting properties that enable future plastic deformation (possibly astate where organic chains remain before pyrolysis). The preliminarybaking is performed preferably at a temperature from 80° C. to 250° C.in order to reliably cause the above phenomena. The formation of theprecursor layer 30 a in accordance with the spin coating technique andthe preliminary baking are repeated for a plurality of times, so thatthe oxide layer 30 has desired thickness.

(b) Main Baking

The precursor layer 30 a is thereafter heated for a predetermined timeperiod in the oxygen atmosphere (e.g. 100% by volume, although being notlimited thereto) at a temperature in the range from 520° C. to 650° C.so as to be mainly baked. As shown in FIG. 4, there is thus formed theoxide layer 30 consisting of bismuth (Bi) and niobium (Nb) (possiblycontaining inevitable impurities; this applies hereinafter) on theelectrode layer. The main baking in accordance with the solutiontechnique is performed in order to form the oxide layer at a heatingtemperature from 520° C. to 650° C., although this upper limit is notfixed to such a degree. The heating temperature exceeding 650° C.stimulates crystallization of the oxide layer and tends to causeremarkable increase in amount of leakage current. The heatingtemperature is thus preferably set not to exceed 650° C. The heatingtemperature less than 520° C. causes carbon in the solvent and thesolute in the precursor solution to remain and causes remarkableincrease in amount of leakage current. The heating temperature is thuspreferably set in the range from 520° C. to 650° C.

The oxide layer 30 is preferably at least 30 nm in thickness. If theoxide layer 30 is less than 30 nm in thickness, the leakage current anddielectric loss increase due to decrease in thickness. It is impracticaland thus not preferred for a solid-state electronic device to includesuch an oxide layer.

Table 1 indicates measurement results on the relationship among theatomic composition ratio between bismuth (Bi) and niobium (Nb) in theoxide layer 30, relative permittivity at 1 KHz, and a leakage currentvalue upon applying 0.5 MV/cm.

TABLE 1 Relative Leakage permittivity current (A/cm²) Nb/Bi ratio (1KHz) (0.5 MV/cm) 3.3 62 1.4 × 10⁻⁶ 2.0 134 2.5 × 10⁻⁴ 1.1 201 5.8 × 10⁻⁶0.8 137 4.2 × 10⁻⁶

The atomic composition ratio between bismuth (Bi) and niobium (Nb) wasobtained by performing elementary analysis on bismuth (Bi) and niobium(Nb) in accordance with the Rutherford backscattering spectrometry(RBS). The methods of measuring the relative permittivity and theleakage current value are to be detailed later. Table 1 indicates theresults of the relative permittivity upon applying the AC voltage of 1KHz and the leakage current value upon applying the voltage of 0.5MV/cm. According to Table 1, when the atomic composition ratio betweenbismuth (Bi) and niobium (Nb) in the oxide layer 30 is in the range from0.8 to 3.3 relative to bismuth (Bi) assumed to be one, the relativepermittivity and the leakage current value had appropriate values for adevice.

(3) Formation of Upper Electrode Layer

The upper electrode layer 40 is subsequently formed on the oxide layer30. FIG. 5 shows the step of forming the upper electrode layer 40. Thepresent embodiment exemplifies a case where the upper electrode layer 40in the thin film capacitor 100 is made of platinum (Pt). Similarly tothe lower electrode layer 20, the upper electrode layer 40 made ofplatinum (Pt) is formed on the oxide layer 30 in accordance with theknown sputtering technique.

The solid-state electronic device according to the present embodimentincludes the oxide layer that is formed by heating, in an atmospherecontaining oxygen, the precursor layer obtained from the precursorsolution as a start material including both the precursor containingbismuth (Bi) and the precursor containing niobium (Nb) as solutes, theoxide layer consisting of bismuth (Bi) and niobium (Nb). Furthermore,the oxide layer is formed by heating at a heating temperature from 520°C. to 650° C. These features lead to preferred electrical properties.Furthermore, the precursor solution for the oxide layer has only to beheated in an atmosphere containing oxygen without adopting the vacuumprocess. Accordingly, increase in area is facilitated and improvementfrom the industrial and mass productivity perspectives can besignificantly achieved in comparison to the conventional sputteringtechnique.

Second Embodiment 1. Entire Configuration of Thin Film CapacitorAccording to the Present Embodiment

A thin film capacitor exemplifying a solid-state electronic deviceaccording to the present embodiment includes a lower electrode layer andan upper electrode layer each of which is made of conductive oxide(possibly containing inevitable impurities) such as metal oxide. FIG. 10shows an entire configuration of a thin film capacitor 200 exemplifyingthe solid-state electronic device according to the present embodiment.The present embodiment is similar to the first embodiment except thatthe lower electrode layer and the upper electrode layer are each made ofconductive oxide such as metal oxide. In the configurations according tothe present embodiment, those corresponding to the configurationsdepicted in FIG. 1 are denoted by the same reference signs and are notdescribed repeatedly, and those different from the configurationsdepicted in FIG. 1 are to be described below. As shown in FIG. 10, thethin film capacitor 200 includes the substrate 10, a lower electrodelayer 220, the oxide layer 30 serving as an insulating layer made of adielectric substance, and an upper electrode layer 240. The lowerelectrode layer 220, the oxide layer 30, and the upper electrode layer240 are stacked on the substrate 10 in this order.

Examples of the lower electrode layer 220 and the upper electrode layer240 can include an oxide layer consisting of lanthanum (La) and nickel(Ni), an oxide layer consisting of antimony (Sb) and tin (Sn), and anoxide layer consisting of indium (In) and tin (Sn) (possibly containinginevitable impurities; this applies hereinafter).

2. Steps of Producing Thin Film Capacitor 200

Described next is a method of producing the thin film capacitor 200.FIGS. 6 to 9 are sectional schematic views each showing a process in themethod of producing the thin film capacitor 200. As shown in FIGS. 6 and7, the lower electrode layer 220 is initially formed on the substrate10. The oxide layer 30 is then formed on the lower electrode layer 220,and the upper electrode layer 240 is subsequently formed. In the stepsof producing the thin film capacitor 200, those similar to the stepsaccording to the first embodiment are not described repeatedly.

(1) Formation of Lower Electrode Layer

FIGS. 6 and 7 each show the step of forming the lower electrode layer220. The present embodiment exemplifies a case where the lower electrodelayer 220 in the thin film capacitor 200 is a conducting oxide layerconsisting of lanthanum (La) and nickel (Ni). The lower electrode layer220 is formed through (a) the step of forming and preliminarily bakingthe precursor layer and then (b) the main baking step.

(a) Formation and Preliminary Baking of Precursor Layer

As shown in FIG. 6, formed on the substrate 10 in accordance with theknown spin coating technique is a lower electrode layer precursor layer220 a obtained from a precursor solution as a start material includingboth a precursor containing lanthanum (La) and a precursor containingnickel (Ni) as solutes (called a lower electrode layer precursorsolution; hereinafter, this applied to a solution of a lower electrodelayer precursor). Examples of the precursor containing lanthanum (La)for the lower electrode layer 220 include lanthanum acetate. Theexamples also possibly include lanthanum nitrate, lanthanum chloride,and any lanthanum alkoxide (e.g. lanthanum isopropoxide, lanthanumbutoxide, lanthanum ethoxide, or lanthanum methoxyethoxide). Examples ofthe precursor containing nickel (Ni) for the lower electrode layerprecursor layer 220 a include nickel acetate. The examples also possiblyinclude nickel nitrate, nickel chloride, and any nickel alkoxide (e.g.nickel indium isopropoxide, nickel butoxide, nickel ethoxide, or nickelmethoxyethoxide).

When the lower electrode layer is a conducting oxide layer consisting ofantimony (Sb) and tin (Sn), examples of a lower electrode layerprecursor containing antimony (Sb) possibly include antimony acetate,antimony nitrate, antimony chloride, and any antimony alkoxide (e.g.antimony isopropoxide, antimony butoxide, antimony ethoxide, or antimonymethoxyethoxide). Examples of a precursor containing tin (Sn) possiblyinclude tin acetate, tin nitrate, tin chloride, and any tin alkoxide(e.g. antimony isopropoxide, antimony butoxide, antimony ethoxide, orantimony methoxyethoxide). When the lower electrode layer is made ofconducting oxide consisting of indium (In) and tin (Sn), examples of aprecursor containing indium (In) possibly include indium acetate, indiumnitrate, indium chloride, and any indium alkoxide (e.g. indiumisopropoxide, indium butoxide, indium ethoxide, or indiummethoxyethoxide). Examples of a lower electrode layer precursorcontaining tin (Sn) are similar to those listed above.

The preliminary baking is then performed in an atmosphere containingoxygen for a predetermined time period at a temperature in the rangefrom 80° C. to 250° C., for the same reason on the oxide layer accordingto the first embodiment. The formation of the lower electrode layerprecursor layer 220 a in accordance with the spin coating technique andthe preliminary baking are repeated for a plurality of times, so thatthe lower electrode layer 220 has desired thickness.

(b) Main Baking

The lower electrode layer precursor layer 220 a is then heated to 550°C. for about 20 minutes in the oxygen atmosphere so as to be mainlybaked. As shown in FIG. 7, there is thus formed, on the substrate 10,the lower electrode layer 220 consisting of lanthanum (La) and nickel(Ni) (possibly containing inevitable impurities; this applieshereinafter). The main baking in accordance with the solution techniqueis performed in order to form the conducting oxide layer preferably at aheating temperature from 520° C. to 650° C., for the same reason on theoxide layer according to the first embodiment. The conducting oxidelayer consisting of lanthanum (La) and nickel (Ni) is also called an LNOlayer.

(2) Formation of Oxide Layer Serving as Insulating Layer

The oxide layer 30 is subsequently formed on the lower electrode layer220. Similarly to the first embodiment, the oxide layer 30 according tothe present embodiment is formed through (a) the step of forming andpreliminarily baking the precursor layer and then (b) the main bakingstep. FIG. 8 shows the state where the oxide layer 30 is formed on thelower electrode layer 220. Similarly to the first embodiment, the oxidelayer 30 is preferably at least 30 nm in thickness.

(3) Formation of Upper Electrode Layer

As shown in FIGS. 9 and 10, the upper electrode layer 240 issubsequently formed on the oxide layer 30. The present embodimentexemplifies a case where the upper electrode layer 240 in the thin filmcapacitor 200 is a conducting oxide layer consisting of lanthanum (La)and nickel (Ni), similarly to the lower electrode layer 220. Similarlyto the lower electrode layer 220, the upper electrode layer 240 isformed through (a) the step of forming and preliminarily baking theprecursor layer and then (b) the main baking step. FIG. 9 shows a lowerelectrode layer precursor layer 240 a formed on the oxide layer 30. FIG.10 shows the upper electrode layer 240 formed on the oxide layer 30.

The solid-state electronic device according to the present embodimentalso includes the oxide layer that is formed by heating, in anatmosphere containing oxygen, the precursor layer obtained from theprecursor solution as a start material including both the precursorcontaining bismuth (Bi) and the precursor containing niobium (Nb) assolutes, the oxide layer consisting of bismuth (Bi) and niobium (Nb).Furthermore, the oxide layer is formed by heating at a heatingtemperature from 520° C. to 650° C. These features lead to preferredelectrical properties. Furthermore, the precursor solution for the oxidelayer has only to be heated in an atmosphere containing oxygen withoutadopting the vacuum process. Improvement can be thus achieved from theindustrial and mass productivity perspectives. Furthermore, the lowerelectrode layer, the oxide layer serving as an insulating layer, and theupper electrode layer are each made of metal oxide and all the steps canbe executed in an atmosphere containing oxygen without adopting thevacuum process. Accordingly, increase in area is facilitated andimprovement from the industrial and mass productivity perspectives canbe significantly achieved in comparison to the conventional sputteringtechnique.

Third Embodiment 1. Entire Configuration of Thin Film CapacitorAccording to the Present Embodiment

Imprinting is performed in the step of forming every one of the layersin a thin film capacitor exemplifying a solid-state electronic deviceaccording to the present embodiment. FIG. 11 shows an entireconfiguration of a thin film capacitor 300 exemplifying the solid-stateelectronic device according to the present embodiment. The presentembodiment is similar to the second embodiment except that the lowerelectrode layer and the oxide layer are imprinted. In the configurationsaccording to the present embodiment, those corresponding to theconfigurations depicted in FIG. 10 are denoted by the same referencesigns and are not described repeatedly, and those different from theconfigurations depicted in FIG. 10 are to be described below. As shownin FIG. 11, the thin film capacitor 300 includes the substrate 10, alower electrode layer 320, an oxide layer 330 serving as an insulatinglayer made of a dielectric substance, and an upper electrode layer 340.The lower electrode layer 220, the oxide layer 330, and the upperelectrode layer 340 are stacked on the substrate 10 in this order.

In this application, “imprinting” is also called “nanoimprinting”.

2. Steps of Producing Thin Film Capacitor 300

Described next is a method of producing the thin film capacitor 300.FIGS. 12 to 21 are sectional schematic views each showing a process inthe method of producing the thin film capacitor 300. Initially formed onthe substrate 10 of the thin film capacitor 300 is the imprinted lowerelectrode layer 320. The imprinted oxide layer 330 is subsequentlyformed on the lower electrode layer 320. The upper electrode layer 340is then formed on the oxide layer 330. In the steps of producing thethin film capacitor 300, those similar to the steps according to thesecond embodiment are not described repeatedly.

(1) Formation of Lower Electrode Layer

The present embodiment exemplifies a case where the lower electrodelayer 320 in the thin film capacitor 300 is a conducting oxide layerconsisting of lanthanum (La) and nickel (Ni). The lower electrode layer320 is formed through (a) the step of forming and preliminarily bakingthe precursor layer, (b) the imprinting step, and (c) the main bakingstep, in this order. Initially formed on the substrate 10 in accordancewith the known spin coating technique is a lower electrode layerprecursor layer 320 a obtained from a lower electrode layer precursorsolution as a start material including both a precursor containinglanthanum (La) and a precursor containing nickel (Ni) as solutes.

The lower electrode layer precursor layer 320 a is then heated in anatmosphere containing oxygen for a predetermined time period at atemperature in the range from 80° C. to 250° C. so as to bepreliminarily baked. The formation of the lower electrode layerprecursor layer 320 a in accordance with the spin coating technique andthe preliminary baking are repeated for a plurality of times, so thatthe lower electrode layer 320 has desired thickness.

(b) Imprinting

As shown in FIG. 12, the imprinting is subsequently performed using alower electrode layer mold M1 with a pressure from 1 MPa to 20 MPa whilethe lower electrode layer precursor layer 320 a is heated at atemperature in the range from 80° C. to 300° C. so as to pattern thelower electrode layer precursor layer 320 a. Examples of a heatingmethod for the imprinting include a method of causing an atmosphere at apredetermined temperature using a chamber, an oven, or the like, amethod of heating a base provided thereon with the substrate from belowusing a heater, and a method of imprinting using a mold preliminarilyheated to a temperature from 80° C. to 300° C. In view ofprocessability, the imprinting is more preferably performed inaccordance with the method of heating a base from below using a heater,as well as using a mold preliminarily heated to a temperature from 80°C. to 300° C.

The mold heating temperature is set in the range from 80° C. to 300° C.for the following reasons. If the heating temperature for the imprintingis less than 80° C., the temperature of the lower electrode layerprecursor layer 320 a is decreased so that plastic deformability of thelower electrode layer precursor layer 320 a is deteriorated. This leadsto lower moldability during formation of an imprinted structure, orlower reliability or stability after the formation. In contrast, if theheating temperature for the imprinting exceeds 300° C., decomposition oforganic chains (oxidative pyrolysis) exerting plastic deformabilityproceeds and thus the plastic deformability is deteriorated. In view ofthe above, according to a more preferred aspect, the lower electrodelayer precursor layer 320 a is heated at a temperature in the range from100° C. to 250° C. for the imprinting.

The imprinting can be performed with a pressure in the range from 1 MPato 20 MPa so that the lower electrode layer precursor layer 320 a isdeformed so as to follow the shape of the surface of the mold. It isthus possible to highly accurately form a desired imprinted structure.The pressure to be applied for the imprinting is set in such a low rangefrom 1 MPa to 20 MPa. In this case, the mold is unlikely to be damagedduring the imprinting and increase in area can be also achievedadvantageously.

The lower electrode layer precursor layer 320 a is then entirely etched.As shown in FIG. 13, the lower electrode layer precursor layer 320 a isthus entirely removed in the regions other than a region correspondingto the lower electrode layer (the step of entirely etching the lowerelectrode layer precursor layer 320 a).

In this imprinting, preferably, a mold separation process ispreliminarily performed on the surface of each of the precursor layersto be in contact with an imprinting surface and/or on the imprintingsurface of the mold, and each of the precursor layers is then imprinted.Such a process is performed. Frictional force between each of theprecursor layers and the mold can be thus decreased, so that theprecursor layer can be imprinted with higher accuracy. Examples of amold separation agent applicable in the mold separation process includesurface active agents (e.g. a fluorochemical surface active agent, asilicon surface active agent, and a non-ionic surface active agent), anddiamond-like carbon containing fluorine.

(c) Main Baking

The lower electrode layer precursor layer 320 a is then mainly baked. Asshown in FIG. 14, there is thus formed, on the substrate 10, the lowerelectrode layer 320 consisting of lanthanum (La) and nickel (Ni)(possibly containing inevitable impurities; this applies hereinafter).

(2) Formation of Oxide Layer Serving as Insulating Layer

The oxide layer 330 serving as an insulating layer is subsequentlyformed on the lower electrode layer 320. The oxide layer 330 is formedthrough (a) the step of forming and preliminarily baking the precursorlayer, (b) the imprinting step, and (c) the main baking step, in thisorder. FIGS. 15 to 18 each show the step of forming the oxide layer 330.

(a) Formation and Preliminary Baking of Precursor Layer

As shown in FIG. 15, similarly to the second embodiment, formed on thesubstrate 10 and the patterned lower electrode layer 320 is a precursorlayer 330 a obtained from a precursor solution as a start materialincluding both a precursor containing bismuth (Bi) and a precursorcontaining niobium (Nb) as solutes. The precursor layer 330 a is thenpreliminarily baked in an atmosphere containing oxygen in the statewhere the precursor layer 330 a is heated to a temperature from 80° C.to 250° C.

(b) Imprinting

As shown in FIG. 16, the precursor layer 330 a only preliminarily bakedis imprinted in the present embodiment. Specifically, the imprinting isperformed using an insulating layer mold M2 with a pressure from 1 MPato 20 MPa in the state where the precursor layer 330 a is heated to atemperature from 80° C. to 300° C. so as to pattern the oxide layer.

The precursor layer 330 a is then entirely etched. As shown in FIG. 17,the precursor layer 330 a is thus entirely removed in the regions otherthan a region corresponding to the oxide layer 330 (the step of entirelyetching the precursor layer 330 a). The step of etching the precursorlayer 330 a in the present embodiment is executed in accordance with thewet etching technique without adopting the vacuum process. The etchingcan be possibly performed using plasma, in accordance with the so-calleddry etching technique.

(c) Main Baking

Similarly to the second embodiment, the precursor layer 330 a is thenmainly baked. As shown in FIG. 18, the oxide layer 330 serving as aninsulating layer (possibly containing inevitable impurities; thisapplies hereinafter) is thus formed on the lower electrode layer 320.The precursor layer 330 a is heated in the oxygen atmosphere for apredetermined time period at a temperature in the range from 520° C. to650° C. so as to be mainly baked.

The step of entirely etching the precursor layer 330 a can be executedafter the main baking. As described above, according to a more preferredaspect, the step of entirely etching the precursor layer is executedbetween the imprinting step and the main baking step. This is becausethe unnecessary region can be removed more easily than the case ofetching each precursor layer after the main baking.

(3) Formation of Upper Electrode Layer

Similarly to the lower electrode layer 320, subsequently formed on theoxide layer 330 in accordance with the known spin coating technique isan upper electrode layer precursor layer 340 a obtained from a precursorsolution as a start material including both a precursor containinglanthanum (La) and a precursor containing nickel (Ni) as solutes. Theupper electrode layer precursor layer 340 a is then heated in anatmosphere containing oxygen at a temperature in the range from 80° C.to 250° C. so as to be preliminarily baked.

As shown in FIG. 19, the upper electrode layer precursor layer 340 ahaving been preliminarily baked is subsequently imprinted using an upperelectrode layer mold M3 with a pressure from 1 MPa to 20 MPa in thestate where the upper electrode layer precursor layer 340 a is heated toa temperature from 80° C. to 300° C. so as to pattern the upperelectrode layer precursor layer 340 a. As shown in FIG. 20, the upperelectrode layer precursor layer 340 a is then entirely etched so thatthe upper electrode layer precursor layer 340 a is entirely removed inthe regions other than a region corresponding to the upper electrodelayer 340.

As shown in FIG. 21, the upper electrode layer precursor layer 340 a isthen heated in the oxygen atmosphere for a predetermined time period toa temperature from 530° C. to 600° C. so as to be mainly baked. Theupper electrode layer 340 consisting of lanthanum (La) and nickel (Ni)(possibly containing inevitable impurities; this applies hereinafter) isthus formed on the oxide layer 330.

The solid-state electronic device according to the present embodimentalso includes the oxide layer that is formed by heating, in anatmosphere containing oxygen, the precursor layer obtained from theprecursor solution as a start material including both the precursorcontaining bismuth (Bi) and the precursor containing niobium (Nb) assolutes, the oxide layer consisting of bismuth (Bi) and niobium (Nb).Furthermore, the oxide layer is formed by heating at a heatingtemperature from 520° C. to 650° C. These features lead to preferredelectrical properties. Furthermore, the precursor solution for the oxidelayer has only to be heated in an atmosphere containing oxygen withoutadopting the vacuum process. Accordingly, increase in area isfacilitated and improvement from the industrial and mass productivityperspectives can be significantly achieved in comparison to theconventional sputtering technique.

In the present embodiment, the lower electrode layer 320, the oxidelayer 330 serving as an insulating layer, and the upper electrode layer340 are stacked on the substrate 10 in this order. The imprintedstructure is formed by performing the imprinting. There is thus no needto include a process requiring relatively long time and/or expensiveequipment, such as the vacuum process, a process in accordance with thephotolithography technique, or the ultraviolet irradiation process. Boththe electrode layers and the oxide layer can be thus patterned easily.The thin film capacitor 300 according to the present embodiment isexcellent from the industrial and mass productivity perspectives.

Fourth Embodiment 1. Entire Configuration of Thin Film CapacitorAccording to the Present Embodiment

Imprinting is performed in the step of forming every one of the layersin a thin film capacitor exemplifying a solid-state electronic devicealso according to the present embodiment. FIG. 25 shows an entireconfiguration of a thin film capacitor 400 exemplifying the solid-stateelectronic device according to the present embodiment. Each of a lowerelectrode layer, an oxide layer, and an upper electrode layer accordingto the present embodiment is preliminarily baked after a correspondingprecursor layer is stacked. Each of the precursor layers having beenpreliminarily baked is imprinted and then mainly baked. In theconfigurations according to the present embodiment, those correspondingto the configurations depicted in FIG. 11 are denoted by the samereference signs and are not described repeatedly, and those differentfrom the configurations depicted in FIG. 11 are to be described below.As shown in FIG. 25, the thin film capacitor 400 includes the substrate10, a lower electrode layer 420, an oxide layer 430 serving as aninsulating layer made of a dielectric substance, and an upper electrodelayer 440. The lower electrode layer 420, the oxide layer 430, and theupper electrode layer 440 are stacked on the substrate 10 in this order.

2. Steps of Producing Thin Film Capacitor 400

Described next is a method of producing the thin film capacitor 400.FIGS. 22 to 24 are sectional schematic views each showing a process inthe method of producing the thin film capacitor 400. In order to producethe thin film capacitor 400, initially formed on the substrate 10 is astacked body including a lower electrode layer precursor layer 420 a asa precursor layer of the lower electrode layer 420, a precursor layer430 a of the oxide layer 430, and an upper electrode layer precursorlayer 440 a as a precursor layer of the upper electrode layer 440. Thestacked body is then imprinted and mainly baked. In the steps ofproducing the thin film capacitor 400, those similar to the stepsaccording to the third embodiment are not described repeatedly.

(1) Formation of Stacked Body Including Precursor Layers

As shown in FIG. 22, initially formed on the substrate 10 is the stackedbody including the lower electrode layer precursor layer 420 a as aprecursor layer of the lower electrode layer 420, the precursor layer430 a of the oxide layer 430, and the upper electrode layer precursorlayer 440 a as a precursor layer of the upper electrode layer 440.Similarly to the third embodiment, the present embodiment exemplifies acase where each of the lower electrode layer 420 and the upper electrodelayer 440 in the thin film capacitor 400 is a conducting oxide layerconsisting of lanthanum (La) and nickel (Ni), and the oxide layer 430serving as an insulating layer consists of bismuth (Bi) and niobium(Nb). Initially formed on the substrate 10 in accordance with the knownspin coating technique is the lower electrode layer precursor layer 420a obtained from a lower electrode layer precursor solution as a startmaterial including both a precursor containing lanthanum (La) and aprecursor containing nickel (Ni) as solutes. The lower electrode layerprecursor layer 420 a is then heated in an atmosphere containing oxygenfor a predetermined time period at a temperature in the range from 80°C. to 250° C. so as to be preliminarily baked. The formation of thelower electrode layer precursor layer 420 a in accordance with the spincoating technique and the preliminary baking are repeated for aplurality of times, so that the lower electrode layer 420 has desiredthickness.

The precursor layer 430 a is then formed on the lower electrode layerprecursor layer 420 a having been preliminarily baked. Initially formedon the lower electrode layer precursor layer 420 a is the precursorlayer 430 a obtained from a precursor solution as a start materialincluding both a precursor containing bismuth (Bi) and a precursorcontaining niobium (Nb) as solutes. The precursor layer 430 a is thenheated in an atmosphere containing oxygen for a predetermined timeperiod at a temperature in the range from 80° C. to 250° C. so as to bepreliminarily baked.

Similarly to the lower electrode layer precursor layer 420 a,subsequently formed on the preliminarily baked precursor layer 430 a inaccordance with the known spin coating technique is the upper electrodelayer precursor layer 440 a obtained from a precursor solution as astart material including both a precursor containing lanthanum (La) anda precursor containing nickel (Ni) as solutes. The upper electrode layerprecursor layer 440 a is then heated in an atmosphere containing oxygenat a temperature in the range from 80° C. to 250° C. so as to bepreliminarily baked.

(2) Imprinting

As shown in FIG. 23, the imprinting is subsequently performed using astacked body mold M4 with a pressure from 1 MPa to 20 MPa in the statewhere the stacked body of the precursor layers (420 a, 430 a, and 440 a)is heated at a temperature in the range from 80° C. to 300° C. so as topattern the stacked body of the precursor layers (420 a, 430 a, and 440a).

The stacked body of the precursor layers (420 a, 430 a, and 440 a) isthen entirely etched. As shown in FIG. 24, the stacked body of theprecursor layers (420 a, 430 a, and 440 a) is thus entirely removed inthe regions other than a region corresponding to the lower electrodelayer, the oxide layer, and the upper electrode layer (the step ofentirely etching the stacked body of the precursor layers (420 a, 430 a,and 440 a)).

(3) Main Baking

The stacked body of the precursor layers (420 a, 430 a, and 440 a) issubsequently mainly baked. As shown in FIG. 25, the lower electrodelayer 420, the oxide layer 430, and the upper electrode layer 440 areaccordingly formed on the substrate 10.

The solid-state electronic device according to the present embodimentalso includes the oxide layer that is formed by heating, in anatmosphere containing oxygen, the precursor layer obtained from theprecursor solution as a start material including both the precursorcontaining bismuth (Bi) and the precursor containing niobium (Nb) assolutes, the oxide layer consisting of bismuth (Bi) and niobium (Nb).Furthermore, the oxide layer is formed by heating at a heatingtemperature from 520° C. to 650° C. These features lead to preferredelectrical properties. Furthermore, the precursor solution for the oxidelayer has only to be heated in an atmosphere containing oxygen withoutadopting the vacuum process. Accordingly, increase in area isfacilitated and improvement from the industrial and mass productivityperspectives can be significantly achieved in comparison to theconventional sputtering technique.

In the present embodiment, all the preliminarily baked precursor layersof the oxide layers are imprinted and then mainly baked. It is thuspossible to shorten the steps of forming the imprinted structure.

EXAMPLES

Examples and comparative examples are provided to describe the presentinvention in more detail. The present invention is, however, not limitedto these examples.

In each of the examples and comparative examples, measurement ofphysical properties of a solid-state electronic device and compositionanalysis of a BNO oxide layer were performed in the following manner.

1. Electrical Properties

(1) Leakage Current

The voltage of 0.25 MV/cm was applied between the lower electrode layerand the upper electrode layer to measure current. The measurement wasperformed using the analyzer 4156C manufactured by Agilent Technologies,Inc.

(2) Dielectric Loss (tan δ)

Dielectric loss in each of the examples and the comparative examples wasmeasured in the following manner. The voltage of 0.1 V or the AC voltageof 1 KHz was applied between the lower electrode layer and the upperelectrode layer at a room temperature to measure dielectric loss. Themeasurement was performed using the broadband permittivity measurementsystem 1260-SYS manufactured by TOYO Corporation.

(3) Relative Permittivity

Relative permittivity in each of the examples and the comparativeexamples was measured in the following manner. The voltage of 0.1 V orthe AC voltage of 1 KHz was applied between the lower electrode layerand the upper electrode layer to measure relative permittivity. Themeasurement was performed using the broadband permittivity measurementsystem 1260-SYS manufactured by TOYO Corporation.

2. Content Percentages of Carbon and Hydrogen in BNO Oxide Layer

Elementary analysis was performed using Pelletron 3SDH manufactured byNational Electrostatics Corporation in accordance with the Rutherfordbackscattering spectrometry (RBS), the Hydrogen Forward scatteringSpectrometry (HFS), and the Nuclear Reaction Analysis (NRA), to obtaincontent percentages of carbon and hydrogen in the BNO oxide layeraccording to each of the examples and the comparative examples.

3. Crystal Structure Analysis of BNO Oxide Layer by Cross-Sectional TEMPicture and Electron Beam Diffraction

The BNO oxide layer according to each of the examples and thecomparative examples was observed using a cross-sectional TransmissionElectron Microscopy (TEM) picture and an electron beam diffractionimage. A Miller index and an interatomic distance were obtained from theelectron beam diffraction image of the BNO oxide layer according to eachof the examples and the comparative examples, and fitting with a knowncrystal structure model was performed to analyze the structure. Adoptedas the known crystal structure model was(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇, β-BiNbO₄, or Bi₃NbO₇.

Example 1

A thin film capacitor of the example 1 was produced in accordance withthe production method of the present embodiment. A lower electrode layeris initially formed on a substrate and an oxide layer is formedsubsequently. An upper electrode layer is then formed on the oxidelayer. The substrate is made of highly heat resistant glass. The lowerelectrode layer made of platinum (Pt) was formed on the substrate inaccordance with the known sputtering technique. The lower electrodelayer was 200 nm thick in this case. Bismuth octylate was used as aprecursor containing bismuth (Bi) layer and niobium octylate was used asa precursor containing niobium (Nb) for the oxide layer serving as aninsulating. Preliminary baking was performed by heating to 250° C. forfive minutes. Formation of a precursor layer in accordance with the spincoating technique and the preliminary baking were repeated for fivetimes. The precursor layer was heated to 520° C. for about 20 minutes inthe oxygen atmosphere so as to be mainly baked. The oxide layer 30 wasabout 170 nm thick. The thickness of each of the layers was obtained asa difference in height between each of the layers and the substrate inaccordance with the tracer method. The atomic composition ratio betweenbismuth (Bi) assumed to be one and niobium (Nb) was 1:1 in the oxidelayer. The upper electrode layer made of platinum (Pt) was formed on theoxide layer in accordance with the known sputtering technique. The upperelectrode layer in this case was 100 μm×100 μm in size and 150 nm inthickness. Electrical properties exhibited the leakage current value of3.0×10⁻⁴ A/cm², the dielectric loss of 0.025, and the relativepermittivity of 62. It was possible to obtain, as the composition ofcrystal phases of the BNO oxide layer, both a fine crystal phase of thepyrochlore crystal structure and a crystal phase of the β-BiNbO₄ crystalstructure. More specifically, the pyrochlore crystal structure was foundto be either the (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure orsubstantially identical with or approximate to the (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure.

Example 2

A thin film capacitor according to the example 2 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 520° C. for one hour in the oxygen atmosphere so asto be mainly baked. Electrical properties exhibited the leakage currentvalue of 3.0×10⁻⁸ A/cm², the dielectric loss of 0.01, and the relativepermittivity of 70. It was possible to obtain, as the composition ofcrystal phases of the BNO oxide layer, both a fine crystal phase of thepyrochlore crystal structure and a crystal phase of the β-BiNbO₄ crystalstructure. More specifically, the pyrochlore crystal structure was foundto be either the (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure orsubstantially identical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure. Furthermore, thecarbon content percentage had a small value of at most 1.5 atm %, whichis not more than the detectable limit. The hydrogen content percentagewas 1.6 atm %.

Example 3

A thin film capacitor according to the example 3 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 530° C. for 20 minutes in the oxygen atmosphere soas to be mainly baked. Electrical properties exhibited the leakagecurrent value of 3.0×10⁻⁶ A/cm², the dielectric loss of 0.01, and therelative permittivity of 110. It was possible to obtain, as thecomposition of crystal phases of the BNO oxide layer, both a finecrystal phase of the pyrochlore crystal structure and a crystal phase ofthe β-BiNbO₄ crystal structure. More specifically, the pyrochlorecrystal structure was found to be either the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure or substantiallyidentical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure.

Example 4

A thin film capacitor according to the example 4 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 530° C. for two hours in the oxygen atmosphere so asto be mainly baked. Electrical properties exhibited the leakage currentvalue of 8.8×10⁻⁸ A/cm², the dielectric loss of 0.018, and the relativepermittivity of 170. It was possible to obtain, as the composition ofcrystal phases of the BNO oxide layer, both a fine crystal phase of thepyrochlore crystal structure and a crystal phase of the β-BiNbO₄ crystalstructure. More specifically, the pyrochlore crystal structure was foundto be either the (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure orsubstantially identical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure. Furthermore, thecarbon content percentage had a small value of at most 1.5 atm %, whichis not more than the detectable limit. The hydrogen content percentagewas 1.4 atm %.

Example 5

A thin film capacitor according to the example 5 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 550° C. for one minute in the oxygen atmosphere soas to be mainly baked. Electrical properties exhibited the leakagecurrent value of 5.0×10⁻⁷ A/cm², the dielectric loss of 0.01, and therelative permittivity of 100. It was possible to obtain, as thecomposition of crystal phases of the BNO oxide layer, both a finecrystal phase of the pyrochlore crystal structure and a crystal phase ofthe β-BiNbO₄ crystal structure. More specifically, the pyrochlorecrystal structure was found to be either the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure or substantiallyidentical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure.

Example 6

A thin film capacitor according to the example 6 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 550° C. for 20 minutes in the oxygen atmosphere soas to be mainly baked. Electrical properties exhibited the leakagecurrent value of 1.0×10⁻⁶ A/cm², the dielectric loss of 0.001, and therelative permittivity of 180. It was possible to obtain, as thecomposition of crystal phases of the BNO oxide layer, both a finecrystal phase of the pyrochlore crystal structure and a crystal phase ofthe β-BiNbO₄ crystal structure. More specifically, the pyrochlorecrystal structure was found to be either the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure or substantiallyidentical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure. Furthermore, thecarbon content percentage was at most 1.5 atm % and the hydrogen contentpercentage was at most 1.0 atm %, each of which had a small value of notmore than the detectable limit.

Example 7

A thin film capacitor according to the example 7 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 550° C. for 12 hours in the oxygen atmosphere so asto be mainly baked. Electrical properties exhibited the leakage currentvalue of 2.0×10⁻⁵ A/cm², the dielectric loss of 0.004, and the relativepermittivity of 100. It was possible to obtain, as the composition ofcrystal phases of the BNO oxide layer, both a fine crystal phase of thepyrochlore crystal structure and a crystal phase of the β-BiNbO₄ crystalstructure. More specifically, the pyrochlore crystal structure was foundto be either the (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure orsubstantially identical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure.

Example 8

A thin film capacitor according to the example 8 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 600° C. for 20 minutes in the oxygen atmosphere soas to be mainly baked. Electrical properties exhibited the leakagecurrent value of 7.0×10⁻⁶ A/cm², the dielectric loss of 0.001, and therelative permittivity of 80. It was possible to obtain, as thecomposition of a crystal phase of the BNO oxide layer, a crystal phaseof the β-BiNbO₄ crystal structure.

Example 9

A thin film capacitor according to the example 9 was produced underconditions similar to those of the example 1 except that the precursorlayer was heated to 650° C. for 20 minutes in the oxygen atmosphere soas to be mainly baked. Electrical properties exhibited the leakagecurrent value of 5.0×10⁻³ A/cm², the dielectric loss of 0.001, and therelative permittivity of 95. It was possible to obtain, as thecomposition of a crystal phase of the BNO oxide layer, a crystal phaseof the β-BiNbO₄ crystal structure.

Example 10

A thin film capacitor according to the example 10 was produced inaccordance with the production method of the fourth embodiment. Thesubstrate 10 is made of highly heat resistant glass. Each of lower andupper electrode layers was an oxide layer containing lanthanum (La) andnickel (Ni). Lanthanum acetate was used as a precursor containinglanthanum (La) for each of the lower and upper electrode layers. Anoxide layer consisting of bismuth (Bi) and niobium (Nb) was formed as anoxide layer serving as an insulating layer. Bismuth octylate was used asa precursor containing bismuth (Bi) and niobium octylate was used as aprecursor containing niobium (Nb) for the oxide layer. A precursor layerof the lower electrode layer was initially formed on the substrate andwas preliminarily baked. The preliminary baking was performed by heatingto 250° C. for about five minutes. The formation of the precursor layerin accordance with the spin coating technique and the preliminary bakingwere repeated for five times. A precursor layer of the oxide layerserving as an insulating layer was subsequently formed on the precursorlayer of the lower electrode layer and was heated to 250° C. for aboutfive minutes so as to be preliminarily baked. A precursor layer of theupper electrode layer was then formed on the precursor layer of theoxide layer serving as an insulating layer under conditions similar tothose for the precursor layer of the lower electrode layer. Thepreliminary baking was subsequently performed by heating to 150° C. forabout five minutes. The formation of the precursor layer in accordancewith the spin coating technique and the preliminary baking were repeatedfor five times. A stacked body of these precursor layers was then heatedto 650° C. for 20 minutes in an atmosphere containing oxygen so as to bemainly baked. The oxide layer serving as an insulating layer was 170 nmthick. The atomic composition ratio between bismuth (Bi) assumed to beone and niobium (Nb) was 1:1 in the oxide layer serving as an insulatinglayer. The upper electrode layer and the lower electrode layer wereabout 60 nm thick. The upper electrode layer in this case was 100 μm×100μm in size. Electrical properties exhibited the leakage current value of2.4×10⁻⁵ A/cm², the dielectric loss of 0.015, and the relativepermittivity of 120. It was possible to obtain, as the composition of acrystal phase of the BNO oxide layer, a crystal phase of the β-BiNbO₄crystal structure.

Comparative Example 1

A thin film capacitor according to the comparative example 1 wasproduced under conditions similar to those of the example 1 except thatthe precursor layer was heated to 500° C. for 20 minutes in the oxygenatmosphere so as to be mainly baked. Electrical properties exhibited theleakage current value as large as 1.0×10⁻² A/cm², the dielectric loss of0.001, and the relative permittivity of 100. It was possible to obtain,as the composition of crystal phases of the BNO oxide layer, both a finecrystal phase of the pyrochlore crystal structure and a crystal phase ofthe β-BiNbO₄ crystal structure.

Comparative Example 2

A thin film capacitor according to the comparative example 2 wasproduced under conditions similar to those of the example 1 except thatthe precursor layer was heated to 500° C. for two hours in the oxygenatmosphere so as to be mainly baked. Electrical properties exhibited theleakage current value as large as 1.0×10⁻¹ A/cm², the dielectric loss of0.007, and the relative permittivity of 180. It was possible to obtain,as the composition of crystal phases of the BNO oxide layer, both a finecrystal phase of the pyrochlore crystal structure and a crystal phase ofthe β-BiNbO₄ crystal structure. Furthermore, the carbon contentpercentage was 6.5 atm % and the hydrogen content percentage was 7.8 atm%, each of which had a large value.

Comparative Example 3

In the comparative example 3, a BNO oxide layer serving as an insulatinglayer was formed on a lower electrode layer at a room temperature inaccordance with the known sputtering technique, and was then heattreated at 550° C. for 20 minutes. A thin film capacitor was producedunder conditions similar to those of the example 1, except for the abovecondition. Electrical properties exhibited the leakage current value of1.0×10⁻⁷ A/cm², the dielectric loss of 0.005, and the relativepermittivity of 50. It was possible to obtain, as the composition of acrystal phase of the BNO oxide layer, a fine crystal phase of theBi₃NbO₇ crystal structure. Furthermore, the carbon content percentagewas at most 1.5 atm % and the hydrogen content percentage was at most1.0 atm %, each of which had a small value of not more than thedetectable limit.

Tables 2 and 3 indicate the configuration of the thin film capacitor,the conditions for forming the oxide layer, the obtained electricalproperties, the content percentages of carbon and hydrogen in the BNOoxide layer, and the result of the crystal structure in each of theexamples 1 to 10 and the comparative examples 1 to 3. The “compositionof crystal phases” in Tables 2 and 3 includes a crystal phase and a finecrystal phase. BiNbO₄ in Tables 2 and 3 indicates β-BiNbO₄.

Processing conditions and Example measurement results 1 2 3 4 5 6 7 8 910 Process Solution Solution Solution Solution Solution SolutionSolution Solution Solution Solution technique technique techniquetechnique technique technique technique technique technique techniqueMain baking 520 520 530 530 550 550 550 600 650 650 temperature Mainbaking period 20 minutes 1 hour 20 minutes 2 hour 1 minutes 20 minutes12 hour 20 minutes 20 minutes 20 minutes Electrode layer PlatinumPlatinum Platinum Platinum Platinum Platinum Platinum Platinum PlatinumPlatinum layer layer layer layer layer layer layer layer layer layerDielectric 0.025 0.01 0.01 0.018 0.01 0.001 0.004 0.001 0.001 0.015 loss(1 KHz) Leakage 3.0 × 10⁻⁴ 3.0 × 10⁻⁸ 3.0 × 10⁻⁶ 8.8 × 10⁻⁸ 5.0 × 10⁻⁷1.0 × 10⁻⁶ 2.0 × 10⁻⁵ 7.0 × 10⁻⁶ 5.0 × 10⁻³ 2.4 × 10⁻⁵ current (A/cm²)(0.25 MV/cm) Relative 62 70 110 170 100 180 100 80 95 120 permittivity(1 KHz) Carbon content — At most — At most — At most — — — — percentage(atm %) 1.5 1.5 1.5 Hydrogen content — 1.6 — 1.4 — At most — — — —percentage (atm %) 1.0 Composition of BiNbO₄ BiNbO₄ BiNbO₄ BiNbO₄ BiNbO₄BiNbO₄ BiNbO₄ BiNbO₄ BiNbO₄ BiNbO₄ crystal phases Bi₂Nb₂O₇ Bi₂Nb₂O₇Bi₂Nb₂O₇ Bi₂Nb₂O₇ Bi₂Nb₂O₇ Bi₂Nb₂O₇ Bi₂Nb₂O₇

TABLE 3 Processing conditions Comparative examples and measurementresults 1 2 3 Process Solution Solution Sputtering technique techniquetechnique Main baking 500 500 — temperature Main baking 20 2 hour —period minutes Electrode Platinum Platinum Platinum layer layer layerlayer Dielectric less 0.001 0.007 0.005 (1 KHz) Leakage current 1.0×10⁻² 1.0 ×10⁻¹ 1.0 ×10⁻⁷ (A/cm2) (0.25 KV/cm) Relative permittivity 100180 50 (1 KHz) Carbon content — 6.5 At most 1.5 percentage (atm %)Hydrogen content — 7.8 At most 1.0 percentage (atm %) Composition ofBiNbO₄ BiNbO₄ Bi₃NbO₇ crystal phases Bi₂Nb₂O₇ Bi₂Nb₂O₇1. Electrical Properties(1) Leakage Current

As indicated in Tables 2 and 3, in each of the examples, the leakagecurrent value upon application of 0.25 MV/cm was at most 5.0×10⁻³ A/cm²and the thin film capacitor exhibited sufficient properties as acapacitor. The leakage current in each of the examples was lower thanthose of the comparative examples 1 and 2. It was found that a preferredvalue was obtained when the heating temperature for forming the oxidelayer was set in the range from 520° C. to 650° C. Furthermore, theobtained result was similar to that of the BNO layer formed inaccordance with the sputtering technique in the comparative example 3.

(2) Dielectric Loss (tan δ)

As indicated in Tables 2 and 3, in each of the examples, the dielectricloss at 1 KHz was at most 0.03 and the thin film capacitor exhibitedsufficient properties as a capacitor. The oxide layer according to eachof the examples is formed by baking a precursor solution including botha precursor containing bismuth (Bi) and a precursor containing niobium(Nb) as solutes. In this application, the above method of forming theoxide layer or a different oxide layer by baking a precursor solution asa start material is also called the “solution technique” for theconvenience purpose. An oxide layer formed in accordance with thesolution technique is a preferred insulating layer also in view of smalldielectric loss. Even having the same composition, the oxide layeraccording to each of the examples exhibited a result similar to that ofthe BNO layer formed in accordance with the sputtering technique in thecomparative example 3.

(3) Relative Permittivity

As indicated in Tables 2 and 3, in each of the examples, the relativepermittivity at 1 KHz was at least 60 and the thin film capacitorexhibited sufficient properties as a capacitor. In contrast, the BNOlayer having the Bi₃NbO₇ crystal structure in the comparative example 3exhibited the relative permittivity as low as 50.

2. Content Percentages of Carbon and Hydrogen in BNO Oxide Layer

In each of the examples 2, 4, and 6 in which the main baking temperaturewas in the range from 520° C. to 650° C., the BNO oxide layer had apreferred carbon content percentage of at most 1.5 atm %. The carboncontent percentage obtained in accordance with this measurementtechnique has a lower limit measurement value of about 1.5 atm %, sothat the actual concentration is assumed to be at most the lower limitmeasurement value. It was also found that the carbon content percentagein each of these examples was at a level similar to that of the BNOoxide layer formed in accordance with the sputtering technique in thecomparative example 3. When the main baking temperature is as low as500° C. as in the comparative example 2, carbon in the solvent and thesolute in the precursor solution is assumed to remain. The carboncontent percentage had the value as large as 6.5 atm %. It is regardedthat the leakage current thus had the value as large as 1.0×10⁻¹ A/cm².

In each of the examples 2, 4, and 6 in which the main baking temperaturewas in the range from 520° C. to 650° C., the BNO oxide layer had apreferred hydrogen content percentage of at most 1.6 atm %. The hydrogencontent percentage obtained in accordance with this measurementtechnique has a lower limit measurement value of about 1.0 atm %, sothat the actual concentration in the example 6 is assumed to be at mostthe lower limit measurement value. It was also found that the hydrogencontent percentage in the example 6 was at a level similar to that ofthe BNO oxide layer formed in accordance with the sputtering techniquein the comparative example 3. When the main baking temperature is as lowas 500° C. as in the comparative example 2, hydrogen in the solvent andthe solute in the precursor solution is assumed to remain. The hydrogencontent percentage had the value as large as 7.8 atm %. Such a largehydrogen content percentage is possibly a reason why the leakage currenthad the value as large as 1.0×10⁻¹ A/cm².

3. Crystal Structure Analysis by Cross-Sectional TEM Picture andElectron Beam Diffraction

FIGS. 26( a) and 26(b) are a cross-sectional TEM picture and an electronbeam diffraction image each showing the crystal structure of the BNOoxide layer according to the example 6. FIG. 26( a) is thecross-sectional TEM picture of the BNO oxide layer according to theexample 6. FIG. 26( b) is the electron beam diffraction image in aregion X in the cross-sectional TEM picture of the BNO oxide layer shownin FIG. 26( a). FIGS. 27( a) and 27(b) are a cross-sectional TEM pictureand an electron beam diffraction image each showing the crystalstructure of the oxide layer serving as an insulating layer in thecomparative example 3. FIG. 27( a) is a cross-sectional TEM pictureshowing the crystal structure of the BNO oxide layer according to theexample 3. FIG. 27( b) is the electron beam diffraction image in aregion Y in the cross-sectional TEM picture of the BNO oxide layer shownin FIG. 27( a). From the cross-sectional TEM picture and the electronbeam diffraction image shown in FIGS. 26( a) and 26(b), it was foundthat the BNO oxide layer according to the present example included acrystal phase and an amorphous phase. More particularly, the BNO oxidelayer was found to include a crystal phase, a fine crystal phase, and anamorphous phase. The “fine crystal phase” in this application means acrystal phase that is not uniformly grown from the upper end to thelower end in the thickness direction of a layered material. Furthermore,fitting with a known crystal structure model in accordance with a Millerindex and an interatomic distance indicated that the BNO oxide layer hadat least one of a fine crystal phase of the pyrochlore crystal structureexpressed by a general formula of A₂B₂O₇ (where A is a metal element andB is a transition metal element; this applies hereinafter) and a crystalphase of the triclinic β-BiNbO₄ crystal structure.

The fine crystal phase of the pyrochlore crystal structure and thecrystal phase of the β-BiNbO₄ crystal structure have differentappearance depending on the main baking temperature for the precursorlayer of the oxide layer serving as an insulating layer. As in theexamples 8 to 10, it was possible to obtain a crystal phase of theβ-BiNbO₄ crystal structure when the main baking temperature was 600° C.and 650° C. As in the examples 1 to 7, it was possible to obtain both afine crystal phase of the pyrochlore crystal structure and a crystalphase of the β-BiNbO₄ crystal structure when the main baking temperaturewas 520° C., 530° C., and 550° C. More specifically, it was found thatthe pyrochlore crystal structure was either the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure or substantiallyidentical with or approximate to the(Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5))O₇ structure and the pyrochlorecrystal structure thus configured exerted preferred electricalproperties as an insulating layer of a thin film capacitor. As in theexamples 1 to 7, it was found that the oxide layer serving as aninsulating layer had both a fine crystal phase of the pyrochlore crystalstructure and a crystal phase of the β-BiNbO₄ crystal structure and thusexhibited preferred relative permittivity as an insulating layer of asolid-state electronic device.

In contrast, the oxide layer formed in accordance with the sputteringtechnique in the comparative example 3 had neither a fine crystal phaseof the pyrochlore crystal structure nor a crystal phase of the β-BiNbO₄crystal structure, but had a fine crystal phase of the Bi₃NbO₇ crystalstructure.

As described above, the solid-state electronic device according to eachof the embodiments is produced in accordance with the solution techniqueand includes the BNO oxide layer obtained by heating at the heatingtemperature (the main baking temperature) for forming the oxide layer inthe range from 520° C. to 650° C. The solid-state electronic device thusproduced has the preferred electrical properties of high relativepermittivity and small dielectric loss. Furthermore, the solid-stateelectronic device is produced in accordance with a simple method in arelatively short time period with no need for complex and expensiveequipment such as a vacuum system. These features remarkably contributeto provision of an excellent solid-state electronic device from theindustrial and mass productivity perspectives.

Other Embodiments

The embodiments of the present invention have been described above,although the present invention is not limited to the contents describedabove.

The solid-state electronic device according to each of the embodimentsis suitable for control of large current with low drive voltage. Thesolid-state electronic device according to each of the embodiments caninclude, in addition to the thin film capacitor, a capacitor such as astacked thin film capacitor or a variable capacity thin film capacitor,a metal oxide semiconductor field effect transistor (MOSFET), asemiconductor device such as a nonvolatile memory, a micro totalanalysis system (TAS), and a micro electric mechanical system (MEMS)device such as a micro chemical chip or a DNA chip.

As described above, the above embodiments have been disclosed not forlimiting the present invention but for describing these embodiments.Furthermore, modification examples made within the scope of the presentinvention, inclusive of other combinations of the embodiments, will bealso included in the scope of the patent claims.

The invention claimed is:
 1. A solid-state electronic device comprising:an oxide layer that is formed by heating, in an atmosphere containingoxygen, a precursor layer obtained from a precursor solution as astarting material including both a precursor containing bismuth (Bi) anda precursor containing niobium (Nb) as solutes, the oxide layerconsisting essentially of the bismuth (Bi) and the niobium (Nb); whereinthe oxide layer has a crystal phase of a pyrochlore crystal structure.2. The solid-state electronic device according to claim 1, wherein theoxide layer has a carbon content percentage of at most 1.5 atm %.
 3. Thesolid-state electronic device according to claim 1, wherein theprecursor layer is provided with an imprinted structure by imprintingthe precursor layer while the precursor layer is heated at a temperaturefrom 80° C. to 300° C. in an atmosphere containing oxygen before theoxide layer is formed.
 4. The solid-state electronic device according toclaim 3, wherein the imprinting is performed with a pressure in a rangefrom 1 MPa to 20 MPa.
 5. The solid-state electronic device according toclaim 3, wherein the imprinting is performed using a mold that ispreliminarily heated to a temperature in a range from 80° C. to 300° C.6. The solid-state electronic device according to claim 1, wherein thesolid-state electronic device is a capacitor.
 7. A solid-stateelectronic device comprising: an oxide layer that is formed by heating,in an atmosphere containing oxygen, a precursor layer obtained from aprecursor solution as a starting material including both a precursorcontaining bismuth (Bi) and a precursor containing niobium (Nb) assolutes, the oxide layer consisting of the bismuth (Bi) and the niobium(Nb); wherein the oxide layer has a crystal phase of a pyrochlorecrystal structure.
 8. The solid-state electronic device according toclaim 7, wherein the precursor layer is provided with an imprintedstructure by imprinting the precursor layer while the precursor layer isheated at a temperature from 80° C. to 300° C. in an atmospherecontaining oxygen before the oxide layer is formed.
 9. The solid-stateelectronic device according to claim 8, wherein the imprinting isperformed with a pressure in a range from 1 MPa to 20 MPa.
 10. Thesolid-state electronic device according to claim 8, wherein theimprinting is performed using a mold that is preliminarily heated to atemperature in a range from 80° C. to 300° C.
 11. The solid-stateelectronic device according to claim 7, wherein the solid-stateelectronic device is a capacitor.